The shift to the Cu/low-k interconnect scheme requires the development of diffusion barrier/adhesion promoter materials that provide excellent performance in preventing the diffusion and intermixing of Cu into the adjacent dielectrics. The integration of Cu with low-k materials may decrease RC delays in signal propagation but pose additional problems because such materials are often porous and contain significant amounts of carbon. Therefore barrier metal diffusion into the dielectric and the formation of interfacial carbides and oxides are of significant concern. The objective of the present research is to investigate the fundamental surface interactions between diffusion barriers and various low-k dielectric materials. Two major diffusion barriers¾ tatalum (Ta) and titanium nitride (TiN) are prepared by DC magnetron sputtering and metal-organic chemical vapor deposition (MOCVD), respectively. Surface analytical techniques, such as X-ray photoelectronic spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are employed. Ta sputter-deposited onto a Si-O-C low dielectric constant substrate forms a reaction layer composed of Ta oxide and TaC. The composition of the reaction layer varies with deposition rate (1 Å-min-1 vs. 2 Å-sec-1), but in both cases, the thickness of the TaC layer is found to be at least 30 Å on the basis of XPS spectra, which is corroborated with cross-sectional TEM data. Sputter-deposited Cu will not wet the TaC layer and displays facile agglomeration, even at 400 K. Deposition for longer time at 2 Å-sec-1 results in formation of a metallic Ta layer. Sputter deposited Cu wets (grows conformally) on the metallic Ta surface at 300 K, and resists significant agglomeration at up to ~ 600 K. Cu diffusion into the substrate is not observed up to 800 K in the UHV environment. Tetrakis(diethylamido) titanium (TDEAT) interactions with SiO2, Cu and a variety of low-k samples in the presence (~ 10-7 Torr or co-adsorbed) and absence of NH3 result in different products. TDEAT interactions with SiO2 are dominated by Ti interactions with substrate oxygen sites, and that Ti oxide/sub-oxide bond formation can proceed with relatively low activation energy. No Ti carbide or Si carbide formation is observed. Co-adsorption of TDEAT and NH3 on SiO2 at 120K followed by annealing to higher temperature results in enhanced Ti-N bond formation, which is stable against oxidation up to 900K in UHV. Similarly, continuous exposures of TDEAT on SiO2 at 500K in the presence of NH3 exhibit a relatively enhanced Ti-N spectral component. Co-adsorption of NH3 and TDEAT on Cu (poly) surface at 120K, followed by annealing to 500K, results in complete desorption of Ti, N or C-containing species from the Cu substrate. Reaction of TDEAT with a Cu surface at 500K yields a Ti-alkyl species via a b-hydride elimination pathway. TDEAT/Cu interactions are not observably affected by overpressures of NH3 of 10-7 Torr. TDEAT interaction with a porous carbon doped oxide low-k substrate at 700K demonstrates undissociated or partly dissociated Ti-NR species trapped in the dielectrics matrix due to its high porosity. In addition, carbide formation is observed from C(1s) XPS spectra. For a hydrocarbon low-k film, the majority sites (carbon) are highly unreactive towards TDEAT even at higher temperature due to a lack of functional groups to initiate the TDEAT/low-k surface chemistry.

An extremely facile and novel method called spontaneous deposition, to deposit noble metal nanoparticles on a most stable form of carbon (C) i.e. diamond is presented. Nanometer sized particles of such metals as platinum (Pt), palladium (Pd), gold (Au), copper (Cu) and silver (Ag) could be deposited on boron-doped (B-doped) polycrystalline diamond films grown on silicon (Si) substrates, by simply immersing the diamond/Si sample in hydrofluoric acid (HF) solution containing ions of the corresponding metal. The electrons for the reduction of metal ions came from the Si back substrate. The diamond/Si interfacial ohmic contact was of paramount importance to the observation of the spontaneous deposition process. The metal/diamond (M/C) surfaces were investigated using Raman spectroscopy, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffractometry (XRD). The morphology (i.e. size and distribution) of metal nanoparticles deposits could be controlled by adjusting the metal ion concentration, HF concentration and deposition time. XRD data indicate the presence of textured and strained crystal lattices of Pd for different Pd/C morphologies, which seem to influence the electrocatalytic oxidation of formaldehyde (HCHO). The sensitivity of electrocatalytic reactions to surface crystal structure implies that M/C could be fabricated for specific electrocatalytic applications. The research also presents electroplating of Cu on ruthenium (Ru), which a priori is a promising barrier material for Cu interconnects in the sub 0.13 μm generation integrated circuits (ICs). Cu plates on Ru with over 90% efficiency. The electrochemical nucleation and growth studies using the potentiostatic current transient method showed a predominantly progressive nucleation of Cu on Ru. This was also supported by SEM imaging, which showed that continuous thin films of Cu (ca. 400 Å) with excellent conformity could be plated over Ru without dendrite formation. Scotch tape peel tests and SEM on Cu/Ru samples both at room temperature (RT) and after annealing at 800 oC, showed no sign of delamination of the Cu film from Ru indicating strong adhesion. XRD patterns from Cu/Ru samples at RT through 800 oC indicated Cu in its characteristic face centered cubic (fcc) form with (111) phase dominating. Most importantly no new XRD peak emerged, even after annealing to 800 oC showing Cu and Ru did not interact much. The excellent adhesion and lack of metallurgical interactions between Cu and Ru underscored the potential application of Ru as a new Cu diffusion barrier in the next generation ICs.

Dans le contexte énergétique actuel, la thermoélectricité, basée sur la conversion directe de l'énergie thermique en énergie électrique, est en plein essor. Cette technologie, qui permet de récupérer l'énergie perdue sous forme de chaleur au cours de processus industriels, est basée sur l'utilisation de modules thermoélectriques. Ces modules sont constitués de la juxtaposition de branches thermoélectriques, constituées de semi-conducteurs n et p, reliées par des jonctions électriques. Dans la gamme de températures de 300 à 600°C, les matériaux de type skutterudite RM4X12 (R : terre rare, M : métal de transition, X : pnictogène) présentent des propriétés thermoélectriques intéressantes. Cependant, les propriétés aux interfaces entre les jonctions électriques et le matériau thermoélectrique jouent un rôle très important dans la performance des modules thermoélectriques. Il est nécessaire de minimiser les pertes électriques et thermiques au niveau de ces interfaces. De même, en zone chaude principalement, il est impératif de limiter l'inter-diffusion entre les éléments constituant le matériau thermoélectrique et le matériau utilisé pour les connexions électriques. La formation de composés aux interfaces peut, en effet, être à l'origine de la dégradation des propriétés du matériau thermoélectrique. Ces contraintes conduisent à introduire des barrières de diffusion entre le matériau thermoélectrique et les connexions électriques. C'est dans ce contexte que ce situe la présente étude, l'objectif étant d'étudier la potentialité de matériaux à base de nitrure de tantale en tant que barrières de diffusion. Ainsi, des couches minces à base de nitrure de tantale ont été déposées, par le procédé de pulvérisation cathodique, sur les substrats de type skutterudite, CeFe4Sb12, les connexions électriques étant en cuivre. L'efficacité de barrières monocouches, TaN, et tri-couches, TaN/Ta/TaN, a été étudiée, ces couches présentant une épaisseur totale de 1 ou 1,5 µm. La première étape de ce travail a consisté en l'étude de la stabilité thermique du matériau skutterudite afin de déterminer le domaine d'utilisation en température de ce matériau. Dans une seconde étape, la potentialité de monocouches, TaN, et multicouches, TaN/Ta/TaN, en tant que barrières de diffusion a été déterminée à partir d'une étude microstructurale. Les assemblages CeFe4Sb12/barrière/Cu ont été préalablement soumis à des traitements thermiques sous vide à des températures variant de 400 à 600°C. Enfin dans une dernière étape, l'étude théorique des mécanismes de migration a été menée à partir des calculs d'énergies d'incorporation et de migration des atomes étrangers, tels que le cuivre et l'antimoine, dans le nitrure de tantale massif. / Due to the current energy context, thermoelectricity based on the direct conversion of thermal energy into electrical energy is of great interest. Direct conversion of thermal energy to electrical energy requires the use of thermoelectric devices made of n- and p-type semiconductor couples connected by electrical junctions. RM4X12 (R: rare earth, M: transition metal, X: pnictogen) skutterudite compounds have been reported to be promising for thermoelectric applications in the [400-600]°C intermediate temperature range. However the performance of thermoelectric devices is strongly dependent on the joining of thermoelectric couples with metal electrodes as the conversion efficiency is greatly influenced by the contact resistance. High electrical and thermal conductivities are required associated with a high interfacial mechanical strength. Moreover the joining material has to be selected to avoid any interfacial reaction occurring during the device fabrication and use. Diffusion barriers are also needed to limit these interfacial reactions which may be detrimental to the thermoelectric device performance. The aim of this work is to study the efficiency of tantalum nitride based materials as diffusion barriers. TaN single layer and TaN/Ta/TaN multilayers barriers were deposited by sputtering between the CeFe4Sb12 skutterudite substrate and the Cu electrical junction. The inter-diffusion of elements was studied through these mono- and multi-layers, of 1 μm or 1.5 μm in thickness. In a first step, the thermal stability of the skutterudite has been investigated to determine the use temperature range of this material. In a second step the efficiency of TaN and TaN/Ta/TaN layers as diffusion barriers has been determined from a microstructural study. CeFe4Sb12/barrier/Cu stackings were previously annealed under vacuum in the [400-600]°C temperature range. Finally a theoretical study of the migration mechanisms was carried out from the calculations of the incorporation and migration energies of species, more specifically Sb and Cu, in the bulk tantalum nitride.

<p>Nickel based coatings were deposited on copper substrates by two different sputtering techniques from a nickel alloy based target. The substrates used were commercially available copper based substrates for low duty electrical contacts. The coatings were analyzed and evaluated as copper diffusion barriers for electrical contact applications. In addition two types of commercially available electroplated nickel coatings (referred to as type A electroplated coatings and type B electroplated coatings) were characterized for comparison. The Technique I sputtered coatings were deposited using three different substrate bias voltages and two different working gas pressures. The Technique II coatings were deposited using two different substrate bias voltages and two different working gas pressures. All sputtered coatings were deposited at a temperature of 200° C. The quality of the barriers was investigated by analyzing their composition, microstructure, stress, mechanical properties , and surface roughness. The results show that sputtered coatings have polycrystalline structures while the two plated films had (200) orientation and (111) orientation. Both plated coatings contained impurities that originate from chemicals used in the plating baths. The surface of the sputtered coatings reflects the substrate surface, while the electroplated samples on the same substrate (type A coatings) show a smooth mirror like surface and the type B electroplated coatings show a rough surface.</p><p>Technique II sputtered coatings showed the highest hardness in the amount of 13 GPa, followed by electroplated type A coatings with a hardness of about 9 GPa while the Technique I coatings showed hardness of 6-8 GPa. All sputtered coatings exhibited compressive stress while the electroplated type A coatings exhibited tensile stress of almost twice the magnitude.</p><p>In this study it is shown that sputtered nickel based coatings sputtered nickel based coatings are a promising more environmental friendly alternative to electroplated nickel coatings.</p>

Ultrathin, semi-permeable membranes are not only essential in natural systems (membranes of cells or organelles) but they are also important for applications (separation, filtering) in miniaturized devices. <br> Membranes, integrated as diffusion barriers or filters in micron scale devices need to fulfill equivalent requirements as the natural systems, in particular mechanical stability and functionality (e.g. permeability), while being only tens of nm in thickness to allow fast diffusion times. Promising candidates for such membranes are polyelectrolyte multilayers, which were found to be mechanically stable, and variable in functionality.<br> In this thesis two concepts to integrate such membranes in larger scale structures were developed. The first is based on the directed adhesion of polyelectrolyte hollow microcapsules. As a result, arrays of capsules were created. These can be useful for combinatorial chemistry or sensing. This concept was expanded to couple encapsulated living cells to the surface. The second concept is the transfer of flat freestanding multilayer membranes to structured surfaces. We have developed a method that allows us to couple mm2 areas of defect free film with thicknesses down to 50 nm to structured surfaces and to avoid crumpling of the membrane. We could again use this technique to produce arrays of micron size. The freestanding membrane is a diffusion barrier for high molecular weight molecules, while small molecules can pass through the membrane and thus allows us to sense solution properties. We have shown also that osmotic pressures lead to membrane deflection. That could be described quantitatively. / Die Entwicklung von “Labors auf einem Chip” hat in den vergangenen Jahren großes Interesse hervorgerufen. Diese Chips ermöglichen schnelle vor Ort Analytik, wie sie beispielsweise in Arztpraxen oder bei der Schadstoff Überwachung wünschenswert wäre. Die Entwicklung solcher Systeme stellt große Herausforderungen an Forscher verschiedenster Disziplinen. <br> Ein großer Vorteil solcher Systeme sind die verkürzten Reaktionszeiten durch die Verkleinerung der Dimensionen. Membranen, die als Diffusionsbarrieren oder Filter in solche Systeme integriert werden sollen, müssen den Ansprüchen an mechanische Stabilität, Funktionalität (z.B. Permeabilität) bei einer Dicke von einigen 10 nm genügen. Die Reduktion der Membrandicke ist erforderlich um die Diffusionszeiten durch die Membran zu minimieren. Polyelektrolyte sind vielversprechende Kandidaten für solche Membranen, da sie sowohl mechanisch stabil sind, als auch variabel in ihrer Funktionalität In dieser Arbeit werden zwei Konzepte zur Integration solcher Membranen vorgestellt. Das erste Konzept basiert auf der selektiven Adhäsion von Polyelektrolytkapseln auf strukturierten Oberflächen. Für das gewählte Kapselsystem konnte bereits eine große Stabilität und eine breite Funktionalität gezeigt werden. Die Strukturierung wird durch Mikrokontaktdrucken erzielt und führt. zu attraktiven und repulsiven Bereichen auf der Oberfläche. Die Kapesladhäsion findet auf den attraktiven Bereichen statt. Auf diese Weise werden die Kapseln 2-dimensional auf der Oberfläche angeordnet. Die definierte laterale Position der Kapseln ermöglicht Anwendungen in der kombinatorischen Chemie oder der Sensorik.<br> Der makroskopische Transfer von bis zu 50 nm dünnen Polyelektrolytmembranen auf microstrukturierte Substrate ist das zweite präsentierte Konzept zur Integration freistehender Membranen. Dabei entsteht ein großflächiger Bereich (mm2) von Millionen von Hohlräumen mit einem Volumen in der Größe von pL (10-12l). Diese Holräume können mit Reagenzien gefüllt werden. Diese reagieren durch die Membran auf Änderungen in der umgebenden Flüssigkeit. Von besonderem Interesse ist der Aspekt, daß nicht nur eingekapselte Reagenzien als Sensormaterial fungieren können, sondern auch durch die Deformation der Membran Änderungen im osmotischen Druck der Umgebung quantitativ erfaßt werden können.

This thesis investigates the ability of transparent surface coatings to reduce xenon diffusion into plastic scintillators. The motivation for the work is improved radioxenon monitoring equipment, used with in the framework of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. A large part of the equipment used in this context incorporates plastic scintillators which are in direct contact with the radioactive gas to be detected. One problem with such setup is that radioxenon diffuses into the plastic scintillator material during the measurement, resulting in an unwanted memory effect consisting of residual activity left in the detector. In this work coatings of Al2O3 and SiO2, with thicknesses between 20 and 400 nm have been deposited onto flat plastic scintillator samples, and tested with respect to their Xe diffusion barrier capabilities. All tested coatings were found to reduce the memory effect, and 425 nm of Al2O3 showed the most promise. This coating was deposited onto a complete detector. Compared to uncoated detectors, the coated one presented a memory effect reduction of a factor of 1000. Simulations and measurements of the expected light collection efficiency of a coated detector were also performed, since it is important that this property is not degraded by the coating. It was shown that a smooth coating, with a similar refractive index as the one of the plastic, should not significantly affect the light collection and resolution. The resolution of the complete coated detector was also measured, showing a resolution comparable to uncoated detectors. The work conducted in this thesis proved that this coating approach is a viable solution to the memory effect problem, given that the results are reproducible, and that the quality of the coating is maintained over time.

Nickel based coatings were deposited on copper substrates by two different sputtering techniques from a nickel alloy based target. The substrates used were commercially available copper based substrates for low duty electrical contacts. The coatings were analyzed and evaluated as copper diffusion barriers for electrical contact applications. In addition two types of commercially available electroplated nickel coatings (referred to as type A electroplated coatings and type B electroplated coatings) were characterized for comparison. The Technique I sputtered coatings were deposited using three different substrate bias voltages and two different working gas pressures. The Technique II coatings were deposited using two different substrate bias voltages and two different working gas pressures. All sputtered coatings were deposited at a temperature of 200° C. The quality of the barriers was investigated by analyzing their composition, microstructure, stress, mechanical properties , and surface roughness. The results show that sputtered coatings have polycrystalline structures while the two plated films had (200) orientation and (111) orientation. Both plated coatings contained impurities that originate from chemicals used in the plating baths. The surface of the sputtered coatings reflects the substrate surface, while the electroplated samples on the same substrate (type A coatings) show a smooth mirror like surface and the type B electroplated coatings show a rough surface. Technique II sputtered coatings showed the highest hardness in the amount of 13 GPa, followed by electroplated type A coatings with a hardness of about 9 GPa while the Technique I coatings showed hardness of 6-8 GPa. All sputtered coatings exhibited compressive stress while the electroplated type A coatings exhibited tensile stress of almost twice the magnitude. In this study it is shown that sputtered nickel based coatings sputtered nickel based coatings are a promising more environmental friendly alternative to electroplated nickel coatings.

CdTe solar cells in the superstrate configuration have achieved record efficiencies of 16% but those in the substrate configuration have reached efficiencies of only 7.8%. A major reason for the lower efficiency of substrate CdTe solar cells is the poor back contact. In this work, CdTe solar cells of the substrate configuration have been fabricated on flexible metallic substrates. For this type of devices, impurity diffusion out of stainless-steel substrates due to high temperature processing can be a cause for poor cell performance. It is necessary to investigate ways of improving the back contact by trying to mitigate the above factors. In this work, Nitrogen has been incorporated in Molybdenum by RF magnetron sputtering. Nitrogen incorporation has helped achieve a 2% increase in efficiency for the best cell and an improvement of 1.5% on an average.

Cilia are evolutionarily conserved microtubule-based organelles projecting from nearly all vertebrate cells, and ciliary defects result in a variety of human disorders known as ciliopathies. Recent studies have shown that several planar cell polarity (PCP) proteins are essential for cilia functions. Here, we focused on Fritz, known as a novel PCP effector protein in Drosophila, in multi-ciliated cells in the epidermis of Xenopus laevis embryos. To investigate the role of Fritz, using confocal and scanning electron microscopy, we discovered that Fritz localizes along the ciliary axonemes and that knockdown of Fritz causes severe reductions in both axoneme length and number. Then, using pull-downs and mass-spectrometry, we identified Chaperonin Containing T-complex polypeptide 1 (CCT) and septin as interacting partners of Fritz. CCT is the key chaperonin interacting with septins, and both have been implicated in ciliogenesis. Using tagged CCT subunit constructs, we found that the tagged CCTα and CCTε co-localize with Fritz along the ciliary axonemes of multi-ciliated cells. Knockdown of Fritz resulted in the accumulation of CCT at the apical cytoplasm of multi-ciliated cells; however, it was confirmed that Fritz does not affect the CCT holoenzyme assembly. Septins, another interacting partner of Fritz, are novel cytoskeletal elements. Using septin antibodies, we found that endogenous septins also localize along the ciliary axonemes and accumulate in the apical cytoplasm of multi-ciliated cells in Fritz morphants. Similar ciliary defects were observed in septin morphants. Our results reveal that Fritz is essential for ciliogenesis, and that CCT and septin interact with Fritz to control ciliogenesis in Xenopus multi-ciliated cells. Additionally, tubulin acetylation is markedly reduced by Fritz knockdown, suggesting that Fritz affects tubulin acetylation.

abstract: Microwave (MW), thermal, and ultraviolet (UV) annealing were used to explore the response of Ag structures on a Ge-Se chalcogenide glass (ChG) thin film as flexible radiation sensors, and Te-Ti chalcogenide thin films as a material for diffusion barriers in microelectronics devices and processing of metallized Cu. Flexible resistive radiation sensors consisting of Ag electrodes on a Ge20Se80 ChG thin film and polyethylene naphthalate substrate were exposed to UV radiation. The sensors were mounted on PVC tubes of varying radii to induce bending strains and annealed under ambient conditions up to 150 oC. Initial sensor resistance was measured to be ~1012 &Omega;; after exposure to UV radiation, the resistance was ~104 &Omega;. Bending strain and low temperature annealing had no significant effect on the resistance of the sensors. Samples of Cu on Te-Ti thin films were annealed in vacuum for up to 30 minutes and were stable up to 500 oC as revealed using Rutherford backscattering spectrometry (RBS) and four-point-probe analysis. X-ray diffractometry (XRD) indicates Cu grain growth up to 500 oC and phase instability of the Te-Ti barrier at 600 oC. MW processing was performed in a 2.45-GHz microwave cavity on Cu/Te-Ti films for up to 30 seconds to induce oxide growth. Using a calibrated pyrometer above the sample, the temperature of the MW process was measured to be below a maximum of 186 oC. Four-point-probe analysis shows an increase in resistance with an increase in MW time. XRD indicates growth of CuO on the sample surface. RBS suggests oxidation throughout the Te-Ti film. Additional samples were exposed to 907 J/cm2 UV radiation in order to ensure other possible electromagnetically induced mechanisms were not active. There were no changes observed using XRD, RBS or four point probing. / Dissertation/Thesis / M.S. Materials Science and Engineering 2013